Bottom Line:
In vivo restimulation revealed a greater impairment in the proliferative ability of T cells resident in a higher antigen presentation environment.Unexpectedly, the system failed to similarly compensate to the persistent stimulus in vivo at the level of CD69 expression and actin polymerization.This greater responsiveness of T cells residing in a host with a lower level of antigen presentation allows us to demonstrate for the first time an intrinsic tuning process in mature T lymphocytes, albeit one more complex than current theories predict.

ABSTRACTThe quantitative adaptation of receptor thresholds allows cells to tailor their responses to changes in ambient ligand concentration in many biological systems. Such a cell-intrinsic calibration of T cell receptor (TCR) sensitivity could be involved in regulating responses to autoantigens, but this has never been demonstrated for peripheral T cells. We examined the ability of monoclonal naive T cells to modulate their responsiveness differentially after exposure to fourfold different levels of persistent antigen stimulation in vivo. T cells expanded and entered a tolerant state with different kinetics in response to the two levels of stimulation, but eventually adjusted to a similar slow rate of turnover. In vivo restimulation revealed a greater impairment in the proliferative ability of T cells resident in a higher antigen presentation environment. We also observed subtle differences in TCR signaling and in vitro cytokine production consistent with differential adaptation. Unexpectedly, the system failed to similarly compensate to the persistent stimulus in vivo at the level of CD69 expression and actin polymerization. This greater responsiveness of T cells residing in a host with a lower level of antigen presentation allows us to demonstrate for the first time an intrinsic tuning process in mature T lymphocytes, albeit one more complex than current theories predict.

fig3: The quantitative impairment of in vivo responsiveness varies with the level of persistent antigen presentation experienced. (a) 5C.C7,RAG2−/− TCR transgenic cells resident for 22–28 d in the PCC-hi host (▴) proliferate poorer than those resident in the PCC-lo host (○) upon retransfer into a fresh PCC-hi environment. Both the adapted T cells are desensitized relative to naive T cells (□) establishing a hierarchy of adaptations in vivo. Data are averaged over three separate experiments. (b) The expansion of adapted T cells was monitored by CFSE dilution over short intervals of time after transfer of 28-d PCC-hi–adapted (P-hi), PCC-lo–adapted (P-lo), or naive (Nv) T cells into fresh PCC-hi mice. Numbers on the left represent the time points sampled in hours. (c) Quantitative analysis of the CFSE profiles in (b) by the Gett-Hodgkins method. (d) Initiation of cell cycling in the transferred T cells quantitated by the disappearance of the zero division CFSE peak reveals two phases of recruitment in the adapted T cells. Both phases, however, decay at greater rates for the PCC-lo–adapted T cells. Overlay of dotted lines on each curve represent the fitting of those parts of the data to a linear regression.

Mentions:
The restriction of in vivo proliferation in both hosts is consistent with an adaptive process but could also be influenced by T cell density and other environmental influences. To compare the intrinsic in vivo proliferative potential of the two T cell populations, we retransferred 2–3 × 106 purified T cells into fresh PCC-hi hosts. As previously reported (18), PCC-hi–adapted T cells proliferated more slowly than naive T cells to this fresh challenge (Fig. 3 a), reaching a peak expansion of 5–8 × 106 cells (compared with 40–60 × 106 for naive T cells) by 4 d. Interestingly, as early as day 2, T cells recovered from the PCC-lo host seemed to expand faster than the PCC-hi–experienced T cells. Over the next 3 d, PCC-lo–experienced T cells expanded to a two- to threefold higher level (10–19 × 106 cells) than the PCC-hi–adapted T cells, yet significantly lower than naive T cells. The difference in expansion resulted in a 2.09 ×/÷ 1.27-fold (n = 4; P = 0.006) higher plateau level for the PCC-lo–adapted T cells compared with the PCC-hi–adapted cells.

fig3: The quantitative impairment of in vivo responsiveness varies with the level of persistent antigen presentation experienced. (a) 5C.C7,RAG2−/− TCR transgenic cells resident for 22–28 d in the PCC-hi host (▴) proliferate poorer than those resident in the PCC-lo host (○) upon retransfer into a fresh PCC-hi environment. Both the adapted T cells are desensitized relative to naive T cells (□) establishing a hierarchy of adaptations in vivo. Data are averaged over three separate experiments. (b) The expansion of adapted T cells was monitored by CFSE dilution over short intervals of time after transfer of 28-d PCC-hi–adapted (P-hi), PCC-lo–adapted (P-lo), or naive (Nv) T cells into fresh PCC-hi mice. Numbers on the left represent the time points sampled in hours. (c) Quantitative analysis of the CFSE profiles in (b) by the Gett-Hodgkins method. (d) Initiation of cell cycling in the transferred T cells quantitated by the disappearance of the zero division CFSE peak reveals two phases of recruitment in the adapted T cells. Both phases, however, decay at greater rates for the PCC-lo–adapted T cells. Overlay of dotted lines on each curve represent the fitting of those parts of the data to a linear regression.

Mentions:
The restriction of in vivo proliferation in both hosts is consistent with an adaptive process but could also be influenced by T cell density and other environmental influences. To compare the intrinsic in vivo proliferative potential of the two T cell populations, we retransferred 2–3 × 106 purified T cells into fresh PCC-hi hosts. As previously reported (18), PCC-hi–adapted T cells proliferated more slowly than naive T cells to this fresh challenge (Fig. 3 a), reaching a peak expansion of 5–8 × 106 cells (compared with 40–60 × 106 for naive T cells) by 4 d. Interestingly, as early as day 2, T cells recovered from the PCC-lo host seemed to expand faster than the PCC-hi–experienced T cells. Over the next 3 d, PCC-lo–experienced T cells expanded to a two- to threefold higher level (10–19 × 106 cells) than the PCC-hi–adapted T cells, yet significantly lower than naive T cells. The difference in expansion resulted in a 2.09 ×/÷ 1.27-fold (n = 4; P = 0.006) higher plateau level for the PCC-lo–adapted T cells compared with the PCC-hi–adapted cells.

Bottom Line:
In vivo restimulation revealed a greater impairment in the proliferative ability of T cells resident in a higher antigen presentation environment.Unexpectedly, the system failed to similarly compensate to the persistent stimulus in vivo at the level of CD69 expression and actin polymerization.This greater responsiveness of T cells residing in a host with a lower level of antigen presentation allows us to demonstrate for the first time an intrinsic tuning process in mature T lymphocytes, albeit one more complex than current theories predict.

ABSTRACTThe quantitative adaptation of receptor thresholds allows cells to tailor their responses to changes in ambient ligand concentration in many biological systems. Such a cell-intrinsic calibration of T cell receptor (TCR) sensitivity could be involved in regulating responses to autoantigens, but this has never been demonstrated for peripheral T cells. We examined the ability of monoclonal naive T cells to modulate their responsiveness differentially after exposure to fourfold different levels of persistent antigen stimulation in vivo. T cells expanded and entered a tolerant state with different kinetics in response to the two levels of stimulation, but eventually adjusted to a similar slow rate of turnover. In vivo restimulation revealed a greater impairment in the proliferative ability of T cells resident in a higher antigen presentation environment. We also observed subtle differences in TCR signaling and in vitro cytokine production consistent with differential adaptation. Unexpectedly, the system failed to similarly compensate to the persistent stimulus in vivo at the level of CD69 expression and actin polymerization. This greater responsiveness of T cells residing in a host with a lower level of antigen presentation allows us to demonstrate for the first time an intrinsic tuning process in mature T lymphocytes, albeit one more complex than current theories predict.